History of X-ray
1. Discovery by:
Wilhelm Conrad Roentgen………November 8,
1895 in Germany.
First Noble prize in physics………..1901.
2. First radiograph was of the hand of Bertha,
3. The first dental radiograph is attributed to
Friedrich Otto Walkhoff.……January 14, 1896
4. The first intraoral radiograph by Dr. Edmund
Kells with the help of Prof. Brown Ayres was
made in the early spring of 1896 in the USA.
• In conventional radiography, a stationary source
and a planar detector are used to produce a 2D
projection image of the patient.
• The image has intensity proportional to the
amount by which the X-rays are attenuated as they
pass through the body.
Limitations of conventional radiography
• The image resolution is not adequate. So specifying
the exact nature of the tissues in the field of interest is
•Conventional radiography provides no depth
information, as the three dimensional (3D) body
structure is projected onto a two-dimensional (2D)
image and objects seen in the third dimension
superimpose losing detail. Thus the need to develop
tomographic images evolved.
Tomography is a specialized imaging technique
where the two-dimensional image produced
represents only a slice or a section of the three-
The third dimension (slice thickness) can be less
than 1 mm.
Each tomograph (or slice) shows the tissues
within that section sharply defined and in focus.
Structures outside the section are blurred and
out of focus.
Indications of Tomography:
Assessment of jaw height, thickness and texture
before inserting implants.
• Postoperative evaluation of implants.
• Assessment of the size, position and extent of
• Evaluation of grossly comminuted facial
fractures to determine all the fracture sites.
• Assessment of the extent of orbital blow-out
• As an additional investigation of the TMJ and
Conventional tomography has essentially been
superseded in medical radiography by the
development of computed tomography (CT). It
is however still important in dentistry, forming
the basis of dental panoramic tomography.
Dental Panoramic Tomography
Orthopantomography And Rotational
In panoramic tomography, the section or focal
plane is designed to be approximately
horseshoe shaped; corresponding to the
shape of the dental arches.
Produces a single tomographic image of facial
structures including both maxillary and
mandibular arches and their supporting
The radiation dose is relatively low; the dose is
equivalent to about three to four perapical
However, there is distortion and magnification of
the final image.
Image quality is inferior to that of intraoral
History of Computed tomography
The first computerized tomography scanner
was introduced by Godfrey Houndsfield in
In 1979, Godfrey Houndsfield received the
Nobel Prize in medicine.
Advantages of CT:
Provides an axial, coronal and sagittal view of the
tissue. The image can be manipulated by the use of
A three dimensional image of the object can be
Provides a greater geometric and anatomical
precision of the lesion.
The structures of the soft tissue both normal and
pathological are clearly displayed.
Produces clearer images with high contrast
resolution compared to the conventional
Image can be enhanced by the use of IV contrast
At present, CT scanners can obtain slices 0.5 mm
thick. A neck examination from skull base to the
mediastinum can be performed in less than 30
Indications of CT in head and neck area:
1. Fracture lines as it provides the clearest definition
of bone structure.
2. CT is the first choice for a survey of metastatic
nodes in the neck.
3. Intracranial diseases, tumors and trauma.
4. Malignancies of the jaws to delineate the margins
5. View TMJ.
6. Implants placement to assess the height of the
Axial CT image of hyperdense lymph node metastasis (arrow) of
squamous cell carcinoma of the tongue base (bent arrow).
Skull base erosion (arrow) by nasopharyngeal
carcinoma in a 40-year-old man with headache
Limitations of CT:
It is an expensive technique.
Very high density restorations as dental
restorations produce severe artifacts on the
High dose of radiation.
There is an inherent risk with the use of
CBCT is a technical advancement in CT
imaging that uses cone beam geometry and a
flat panel detector (FPD) to provide a
relatively low-dose imaging with resolution
acquired with a single gantry revolution (17).
The first (CBCT) system for dental use was
developed in 1999.
Visualization of the full data
volume by means of a shaded
surface display with the
threshold set to show hard
tissues (bone and teeth) only
The data attenuation values
corresponding to the soft tissues
were made partially transparent,
allowing for visualization of the
underlying skeleton and teeth.
Advantages of CBCT
It provides clear images of highly contrasted structures.
Accurate measurements can be derived from the
Reduced radiation exposure to the patient compared
with medical CT. Imaging doses is approximately onetenth that of a diagnostic CT scan.
Reduced cost compared to CT.
Possibility of office-based compact CBCT scanner suitable
for use in an office-based setting .
CBCT scanner can collect volume data by means of a
single rotation taking 9-40 seconds.
Comparison of(a) sagittal conventional tomography (CVT) images, (b)
helical CT (HCT) images and (c) limited cone beam CT (limited CBCT)
images of the medial region of the mandibular condyle which showed
erosive changes in the superficial soft tissue with anatomical observation.
The findings of resorptive changes in bone cortex were obtained with HCT
and limited CBCT images
Stafne’s bone cavity
Conventional sialogram showing that some branch ducts arising superiorly from
the hilum of the submandibular gland seemed to distribute in the cavity area
Stafne’s bone cavity
3D CBCT sialography shows the spatial relationship of
submandibular gland and the bone cavity
Stenosis of stensen’s duct in sjogren syndrome
shows stenosis of
the right Stensen’s
CBCT sialography with 3D
reconstruction show stenosis
with areas of strictures through
the glandular ductules (arrows).
CBCT in Imaged-Guided Surgery
Imaged guided surgery can
delineate the tumor and
related structures, thereby
and allowing preservation of
adjacent vital structures,
while achieving complete
A mobile C-arm
platform. This is easier
to manage when an
Limitation of CBCT:
Limited image quality in comparison with MSCT.
Less soft tissue visibility compared to MSCT.
But despite these limitations the use of MSCT
associated with much radiation in dentistry
should be avoided in cases where the imaging
ability of the CBCT technique is thought to be
adequate for diagnosis and treatment planning.
Magnetic resonance imaging (MRI) is an
imaging modality that uses the response of
biologic tissues to an applied and changing
magnetic field to generate images.
Advantages of MRI
MRI provides good contrast between the different soft
tissues of the body, which makes it especially useful in
imaging the brain , muscles, the heart, and cancers
compared with other medical imaging techniques such
as CT or X-rays.
Unlike CT scans or traditional X-rays, MRI does not
use ionizing radiation.
No harmful effects are known to occur during pregnancy.
However, as a precaution, pregnant women should
undergo MRI only when essential particularly during the
first trimester of pregnancy.
Applications of MRI
The applications of MRI mostly rely on its
ability to offer improved soft tissue
Perineural infiltration of cranial nerve VII by
adenoid cystic carcinoma.
Image shows vertical
extension of the
(arrows) through the
Disadvantages of MRI:
MRI frequently requires 30 to 45 minutes of
scanning time, during which time the patient
must remain motionless, a process difficult for
sick patient to accomplish. Motion artifacts
are more frequently encountered than with
CT, although dental artifacts may be less
Unfortunately, MRI is one of the most
expensive imaging modalities.
Contraindications of MRI:
Absolute contraindications to MRI
include patients with cardiac pacemakers,
cochlear implants, and ferromagnetic
intracranial aneurysm clips.
Generally, ocular prostheses and ossicular
implants are safe.
Ultrasound (US) images are 2D gray-scale
images. They are based on the phenomenon of
reflection of ultrasound waves.
The tissue that reflects a considerable amount
of ultrasound is described as hyperechoic.
While hypoechoic is the area that reflects less
amount of ultrasound compared to the
adjacent tissue. Anechoic is an area where
there is no reflection of echoes.
Bone surfaces demonstrate total reflection of
ultrasound waves (hyperechoic) thus
structures inside and beyond intact bone are
not normally detectable by ultrasound.
Cystic structures in the other hand are fluid
filled thus anechoic and the ultrasound waves
pass through it with little or no attenuation.
Advantages of Ultrasonography
Ultrasound has no known harmful effects and
no contraindications as it doesn’t use ionizing
It is relatively inexpensive compared with CT
or MRI. It is the easiest to use and the least
Applications of Ultrasound Imaging
US is used for the detection of noninvasive and
soft tissue-related diseases in oral and
maxillofacial regions particularly it is clinically
applied to evaluate salivary gland-related
diseases, lymph node-related diseases,
subcutaneous diseases, and tongue related
It is especially useful in the pediatric population,
due to the relatively superficial nature of the
Intraoperative determination of tumor
thickness and resection margin in tongue
carcinomas using Ultrasonography
Ultrasonographic image of tumor shown as
hypoechoic shadow (preoperative view)
Needle being introduced to indicate
deep surgical margin clearance under
Ultrasonographic image of tumor with
the needle positioned at 10 mm from the
deepest invasive front of the tumor
Red arrows showing the needle.
Resected fresh specimen
Scanning of gelatin-embedded
specimen from superior surface
Ultrasonographic scan of gelatinembedded specimen
H & E stained section of region of
Diagnosis of Metastatic Lymph Nodes in Oral Cancer
The metastatic lymph node (arrows) contacts
the common carotid artery (white arrowheads)
Magnification of the same
area in a CT of the same
Demonstration of salivary gland stones
•Ultrasound is a sensitive imaging modality in the
detection of salivary stones are quoted accuracies of 90%.
•About 20% of salivary stones are radio-lucent on
radiography. With ultrasound it is possible to identify these
stones and to identify their precise location.
Longitudinal section of a dilated submandibular duct (Wharton`s duct)
A stone is located in the anterior portion of the duct
Longitudinal section of the pre-epiglottic space.
A cystic lesion is seen caudal to the hyoid bone:
Thyroglossal duct cyst.
Limitations of Ultrasound imaging:
They include inaccessibility of deep-seated
lesions, its inability to penetrate bone or airfilled structures.
US provides a limited field of view, lack of
easily identifiable anatomic landmarks, and
Less time is required for a CT of the neck to be
done (2-3 min) compared to an US (30 min).
Color Doppler Ultrasonography
Doppler ultrasound assesses the distribution of
vessels within the node.
It is suggested that as color Doppler ultrasound
(CDUS) can differentiate between reactive and
neoplastic lymph nodes.
Thus CDUS can eliminate the need of biopsy/FNAC
in case of reactive lymph nodes. When the results
of CDUS suggest malignancy US guided FNAB is
then required to reach a final diagnosis.
A small ovoid node with hilar vascularity - Typical
reactive lymph node is visualized
A rounded lymph node with multiple peripheral arteries is
visualized in a squamous cell carcinoma lymph node metastasis
Nuclear imaging is a method of producing images
by detecting radiation from different parts of the
body after a radioactive isotope (radionuclide) is
The radionuclide undergoes radioactive decay,
resulting in the emission of gamma rays. External
detectors (gamma cameras) capture and form
images from the radiation emitted.
The main difference between nuclear imaging
and other radiologic tests is that nuclear imaging
assesses how organs function, whereas other
imaging methods assess anatomy.
There are several techniques of diagnostic
nuclear medicine such as:
Positron emission tomography (PET).
Single Photon emission tomography (SPECT).
In Scintigraphy the radioisotopes (here called
radiopharmaceuticals) are taken internally,
and the emitted radiation is captured by
external detectors (gamma cameras) to form
two dimensional images.
Applications of scintigraphy
Detection of sialolithiasis With or Without
Sialolithiasis with functional obstruction of the right
parotid gland without any parenchymal impairment
Sialolithiasis with functional obstruction of the right
parotid gland with parenchymal impairment
PET is a tomography in which a computer-
generated image of metabolic or physiologic
activity within the body is produced through the
detection of gamma rays that are emitted when
introduced radionuclides decay and release
Advantages of PET:
PET can image biochemical and biological
processes that are fundamental to disease.
Since diseases are viewed not only in terms of
structure but also as process, PET can
routinely detect diseases even though
normal results are provided by CT and MRI.
Application of PET
The main application of PET is in the field of
The most commonly used PET radiopharmaceutical
in oncological applications is the glucose analogue
Glucose metabolism in growing neoplastic cells is
enhanced and accounts for the increased uptake on
To monitor treatment from a metabolic perspective.
PET in the diagnosis of Lymphoma
A major problem concerns the systemic nature of
lymphoma and its treatment, which is usually not
Whole body PET has a significant impact on staging
of lymphoma, since biopsy of all lesions is
Same patient after four courses of chemotherapy
Limitations of PET
Although the accuracy of PET is higher than MR
and/or CT, there is lack of correct anatomical
localization of the abnormal PET foci which is
necessary for treatment.
This can be overcome by the use of PET/CT.
PET is considered as an expensive imaging
modality. However, whole body PET appear cost
effective when compared to a more conventional
approach with multiple CT or MR scans of specific
PET/CT is a medical imaging technique using a
device which combines in a single system
both a PET scan and an x-ray CT, so that
images acquired from both devices can be
taken sequentially, in the same session from
the patient and combined into a single
Advantages of PET/CT
Increased sensitivity and specificity in
evaluation of primary and recurrent
The exact localization of a focal abnormality
The superimposition onto an anatomically
identifiable structure makes the image
interpreter more confident and reduces interobserver variability.
Normal whole body PET/CT scan with FDG-18. The whole body PET/CT scan is
commonly used in the detection, staging and follow-up of various cancers.
Abnormal whole body PET/CT scan with multiple metastases from a cancer. The
whole body PET/CT scan has become an important tool in the evaluation of cancer.
Evaluating Carcinoma of Unknown Primary
Subtle difference in uptake between right (arrow) and left tonsil on the
PET/CT of patient with carcinoma of unknown primary—the right
tonsil was subsequently identified as the primary site.
Choice of the appropriate imaging modality
The choice of imaging modality varies depending on
the location and nature of the disease process.
CT is fast and widely available and can be
employed as the first and often the only imaging
modality in the majority of the disease processes
affecting the neck.
CT excels in demonstrating bone detail.
Radiation exposure from CT examination is
substantial and should be taken into account
particularly in young patients who require repeat
MRI provides excellent soft tissue contrast and is
the modality of choice in most aggressive processes.
Successful primary staging of most malignant
lesions in the neck can be accomplished with CT
or MRI and clinical examination.
The accuracy of PET increases when it is used in
conjunction with CT.
PET/CT is superior in identifying distant
metastases and postoperative follow-up.
Image interpretation should always be made in
conjunction with clinical information.